<h2>Problem 211</h2>
<div style="color:#666;font-size:80%;">04 October 2008</div><br />
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<p>For a positive integer <var>n</var>, let &sigma;<img src="" style="display:none;" alt="_(" /><sub>2</sub><img src="" style="display:none;" alt=")" />(<var>n</var>) be the sum of the squares of its divisors. For example,</p>
<div style="text-align:center;">&sigma;<img src="" style="display:none;" alt="_(" /><sub>2</sub><img src="" style="display:none;" alt=")" />(10) = 1 + 4 + 25 + 100 = 130.</div>
<p>Find the sum of all <var>n</var>, 0 <img src='images/symbol_lt.gif' width='10' height='10' alt='&lt;' border='0' style='vertical-align:middle;' /> <var>n</var> <img src='images/symbol_lt.gif' width='10' height='10' alt='&lt;' border='0' style='vertical-align:middle;' /> 64,000,000 such that &sigma;<img src="" style="display:none;" alt="_(" /><sub>2</sub><img src="" style="display:none;" alt=")" />(<var>n</var>) is a perfect square.</p>
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